1. Field of the Invention
The present invention relates to a display apparatus for displaying information by means of a diffraction grating such as a hologram.
2. Related Background Art
U.S. Pat. No. 4,613,200 discloses a display apparatus utilizing the combination of a set of holograms and a display unit, in which the light from the display unit is reflected and diffracted by a hologram toward the other, and is again reflected and diffracted by the other hologram toward the observer so as to enter into the pupil of the observer. Since the optical path length between the display unit and a hologram closer thereto is larger than that between two holograms, said apparatus is associated with drawbacks that the dimension of the entire apparatus is inevitably large and that the viewing zone in which the observer can observe the displayed information is limited.